(a) Field of the Invention
This invention relates to a refrigeration system having at least a freezer unit.
(b) Description of Related Art
In refrigeration systems used in convenience stores, for example, the temperature level for cooling differs for different types of objects being cooled such as foods and drinks. For this reason, refrigeration systems having a chiller unit and a freezer unit are conventionally used.
In a freezer unit, an object being cooled need to be cooled to a lower temperature than in a chiller unit, and therefore a refrigerant must be reduced in pressure to a considerably lower pressure. However, if the refrigerant pressure difference in a refrigerant circuit becomes large, the efficiency of a compressor therein will be decreased. To cope with this, a conventional refrigeration system, as shown in FIG. 7, is provided with a cascade unit (106) having a lower-temperature-side compressor (107) and a cascade condenser (108) separately from a heat source side unit (103) having a heat source side compressor (101) and a heat source side heat exchanger (102), a chiller unit (104) and a freezer unit (105), thereby forming a binary refrigeration cycle. The amount of heat exchange of the cascade condenser (108) depends upon the amount of refrigerant supplied from a receiver (109). Therefore, the amount of heat exchange of the cascade condenser (108) is subject to the operating conditions at that time.
The conventional refrigeration system, however, has its occupying space increased by the placement of the cascade unit (106). Further, its cost is relatively high by the necessity of the cascade condenser (108).
The present invention has been made in view of these circumstances, and therefore its object is to promote space saving and cost reduction for a refrigeration system including a freezer unit and one or more other units.
A refrigeration system according to the present invention is a refrigeration system including a refrigerant circuit formed by connecting at least all of: a heat source side unit having a heat source side compressor and a heat source side heat exchanger; a chiller unit having a chilling heat exchanger for cooling an object being cooled; and a freezer unit having a freezing heat exchanger for cooling an object being cooled at a lower temperature than the chilling heat exchanger, wherein the freezer unit is provided with a freezing compressor for compressing a refrigerant in a total of two stages together with the heat source side compressor.
In the above refrigeration system, the freezer unit is provided with a freezing compressor and a two-stage compression refrigeration cycle is established by the freezing compressor and the heat source side compressor. Accordingly, the system needs no cascade condenser in spite of a so-called multi-circuit type including the chiller unit and the freezer unit, which allows the system to be entirely reduced in size and promotes cost reduction thereof Further, it is possible to avoid a heat loss in the cascade condenser and thereby enhance operating efficiency.
Another refrigeration system according to the present invention is a refrigeration system including a refrigerant circuit formed by connecting at least all of: a heat source side unit having a heat source side compressor and a heat source side heat exchanger; a room air conditioning unit having an indoor heat exchanger for heating or cooling room air; and a freezer unit having a freezing heat exchanger for cooling an object being cooled, wherein the freezer unit is provided with a freezing compressor for compressing a refrigerant in a total of two stages together with the heat source side compressor.
In the above refrigeration system, the freezer unit is provided with a freezing compressor and a two-stage compression refrigeration cycle is established by the freezing compressor and the heat source side compressor. Accordingly, the system needs no cascade condenser in spite of a so-called multi-circuit type including the room air conditioning unit and the freezer unit, which allows the system to be reduced in size and promotes cost reduction thereof Further, it is possible to enhance operating efficiency.
Still another refrigeration system according to the present invention is a refrigeration system including a refrigerant circuit formed by connecting at least all of: a heat source side unit having a heat source side compressor and a heat source side heat exchanger; a room air conditioning unit having an indoor heat exchanger for heating or cooling room air; and a chiller unit having a chilling heat exchanger for cooling an object being cooled; and a freezer unit having a freezing heat exchanger for cooling an object being cooled at a lower temperature than the chilling heat exchanger, wherein the freezer unit is provided with a freezing compressor for compressing a refrigerant in a total of two stages together with the heat source side compressor.
In the above refrigeration system, the freezer unit is provided with a freezing compressor and a two-stage compression refrigeration cycle is established by the freezing compressor and the heat source side compressor. Accordingly, the system needs no cascade condenser in spite of a so-called multi-circuit type including the room air conditioning unit, the chiller unit and the freezer unit, which allows the system to be reduced in size and promotes cost reduction thereof. Further, it is possible to enhance operating efficiency.
The freezer unit may include a pressure reduction mechanism and may be connected to a liquid-side pipe branched from a liquid line of the heat source side unit and a gas-side pipe branched from a gas line of the heat source side unit, and the freezer unit may be constructed so that in a direction from the liquid-side pipe to the gas-side pipe, the pressure reduction mechanism, the freezing heat exchanger and the freezing compressor are connected in this order.
The freezer unit is preferably provided with: an oil separator disposed on the discharge side of the freezing compressor; and an oil return pipe which have a pressure reduction mechanism and connects the oil separator to the suction side of the freezing compressor therethrough.
In the above refrigeration system, an effluent refrigeration oil from the freezing compressor is returned thereto again through the oil separator and the oil return pipe, so that lubrication failure in the freezing compressor can be surely prevented. During the shut-down of the freezing compressor, oil in the oil separator is returned to the suction side of the freezing compressor through the oil return pipe, and therefore there never occurs a phenomenon that during the shut-down, the oil would flow backward to the discharge side of the compressor. Accordingly, the oil never resides at the discharge side of the freezing compressor so that the freezing compressor can be smoothly restarted.
Preferably, the freezing compressor is formed by an inverter compressor, and the oil return pipe in the freezer unit or an inlet pipe of the freezing compressor is provided with a heat exchanger for cooling an inverter in the inverter compressor with at least a refrigeration oil separated by the oil separator.
In the above refrigeration system, since the discharge side of the freezing compressor has a relatively low pressure, it has a relatively low temperature. Therefore, the refrigeration oil returned from the oil separator to the freezing compressor through the oil return pipe also has a relatively low temperature. Since the heat exchanger is provided on the oil return pipe or the inlet pipe, the inverter is cooled through the heat exchange at least with the low-temperature refrigeration oil. As a result, the system is difficult to cause failure due to overheat of the inverter. This enhances the reliability of the freezing compressor.
According to the present invention, no cascade condenser is needed in a refrigeration system of a so-called multi-circuit type that includes a freezer unit and one or more other heat utilization side units. Hence, space saving and cost reduction for the system can be achieved.
If an oil separator is provided on the discharge side of the freezing compressor so that a refrigeration oil separated by the oil separator is recovered into the freezing compressor through the oil return pipe, the reliability of the freezing compressor and further the reliability of the refrigeration system can be enhanced.
If the freezing compressor is formed by an inverter compressor and a heat exchanger is provided for cooling the inverter with at least the refrigeration oil separated by the oil separator, the cold heat of the refrigeration oil can prevent the inverter from overheating. Accordingly, the reliability of the inverter compressor can be enhanced without using any external cooling source, thereby enhancing the reliability of the refrigeration system.